This invention relates to a system for analyzing a vehicle state, such as fuel consumption rate and its analysis method.
JP-A-2000-205925 published by the Japanese Patent Office in 2000 discloses a device for analyzing a vehicle state such as fuel consumption rate. This device computes a consumed fuel flowrate based on a fuel injection pulse signal output from an engine controller, computes a running distance based on a vehicle speed pulse signal output from a vehicle speed sensor, and computes a fuel consumption rate by dividing the computed running distance by the consumed fuel flowrate.
However, this device uses a fuel injection pulse signal for the computation of fuel consumption rate, i.e., it assumes a vehicle provided with an electronic fuel injection device (EGI), and cannot be applied to a non-EGI vehicle or a diesel engine vehicle which does not have a fuel injection pulse signal.
In a method which can be used with a non-EGI vehicle or a diesel engine vehicle, a brake specific fuel consumption is calculated by looking up an engine performance map (a map specifying a relation between an engine running condition and the brake specific fuel consumption), and fuel consumption rate is computed based thereon. However, such an engine performance map does not normally exist, and even if it did it would be difficult to acquire.
It is therefore an object of this invention to allow precise computation of fuel consumption rate without using a fuel injection pulse signal. It is a further object of this invention to provide an objective evaluation criterion of vehicle state by displaying the vehicle state including fuel consumption rate to the driver or manager.
In order to achieve above object, this invention provides a vehicle state analysis system for a vehicle including an engine, comprising a sensor which detects an air-fuel ratio of the exhaust of the engine, and a processor which functions to compute a weight of fuel consumed by the engine based on an intake air amount and the air-fuel ratio of the engine, and compute a fuel consumption rate of the vehicle based on the computed weight of consumed fuel and the running distance of the vehicle.
According to this invention, the weight of fuel consumed by the engine is calculated based on an intake air amount and air-fuel ratio of a vehicle to be analyzed, and fuel consumption rate is computed based on this and on the running distance. The conventional fuel consumption rate computation method used a fuel injection pulse signal and cannot therefore be applied to a vehicle which does not have a fuel injection pulse signal, but as the analysis system according to this invention does not use a fuel injection pulse signal to compute the fuel consumption rate, a computation of fuel consumption can be performed precisely even for a vehicle which does not have a fuel injection pulse signal such as a non-EGI vehicle or a diesel engine vehicle.
A sensor which detects the intake air amount and a sensor which detects the air-fuel ratio which are required for the computation are already installed in the vehicle, so if a system is constructed using these components, the analysis system can be made at low cost. The intake air amount is generally computed based on the intake air flowrate detected by an air flow meter. In another method, the intake air amount may be detected based on the absolute pressure in an intake manifold and the displacement of the engine.
The fuel consumption rate may for example be computed by converting the weight of consumed fuel into a consumed fuel flowrate by dividing by the fuel density, and dividing the running distance by this consumed fuel flowrate. When the vehicle is stationary, the fuel density may vary due to oil supply, etc., so when the vehicle is stationary, the fuel consumption rate may be computed more precisely if the fuel density is corrected.
If the air-fuel ratio is detected by a sensor installed in the exhaust passage of the engine, some time is required until the fuel burnt in the engine reaches the sensor installation position, and the gas in the exhaust passages also disperses, so the detected air-fuel ratio has a delay relative to the actual air-fuel ratio. Therefore, the precision of computing fuel consumption rate may be further improved by computing the weight of consumed fuel taking account of this delay.
If the computed fuel consumption rate is displayed to the driver, the driver can obtain an idea of the vehicle state in terms of specific figures, and this contributes to improving his driving technique. For example, the driver can appreciate ways of driving which impair-fuel cost-performance and ways of driving which improve fuel cost-performance through his own driving, so he can easily learn a way of driving which reduces the fuel consumption. The units used to display fuel consumption rate are generally [km/l], but this may be changed to other units (e.g., [kg/l] or [tonxc2x7km/l]) if necessary. Thus, to make a proper evaluation of fuel cost-performance when the vehicle to be analyzed is a transport truck and it is necessary to consider the effect of the load (total weight of vehicle), for example, [tonxc2x7km/l] may be used. The unit may be changed to another unit, for example [MPG], which is common in the country where this system is used.
If the excess drive force (=present drive forcexe2x88x92running resistance) is displayed to the driver, and the driver is warned during hard braking or acceleration when there is a large effect on fuel cost-performance, in addition to fuel consumption rate, the driver may be made aware of ways of driving which adversely affect fuel cost-performance based on this information. If the reserve drive force (=maximum drive forcexe2x88x92present drive force) is displayed to the driver, the driver may be made aware of how much acceleration performance is still available to him.
It is understood that, to make a precise computation of excess drive force, data such as the total weight of the vehicle or rolling resistance coefficient which is used for the computation, must be precise. If the total weight of the vehicle is corrected taking account of the changes in the total weight of the vehicle which may occur due to load variation when the vehicle is stationary, and if the rolling resistance coefficient is corrected at the timing at which the accelerator is off and the clutch of a transmission is disengaged, the excess drive force can be computed precisely.
The drive force of the vehicle to be analyzed may be computed based on the engine shaft torque calculated by looking up a predetermined map based on the accelerator depression amount and engine rotation speed. When such a map does not exist, it may also be computed by calculating the engine shaft torque based on the brake mean effective pressure obtained by subtracting a friction mean effective pressure according to the engine rotation speed from an indicated mean effective pressure which is calculated from the intake air amount per cycle and air-fuel ratio.
The maximum drive force used to compute the reserve drive force may be computed from the maximum value of the shaft torque which can be acquired from a catalogue, etc. When the maximum value of shaft torque is unclear, the brake mean effective pressure for maximum accelerator depression is computed by subtracting the friction mean effective pressure according to the engine rotation speed from the indicated mean effective pressure for maximum accelerator depression found by computation, the shaft torque for maximum accelerator depression is computed based thereon and the engine displacement, and the maximum drive force may then be computed based on this shaft torque for maximum accelerator depression.
The computed vehicle state (fuel consumption rate, excess drive force, reserve drive force) or selected gear position may be recorded on a record medium, and the data recorded on the record medium may be displayed (e.g., displayed on a display such as a manager""s computer) after running. In this way, the manager can obtain an objective evaluation of the vehicle state, suitably manage the vehicles, select a suitable vehicle according to load and instruct the drivers suitably.